1. Field of the Invention
This invention relates to a hydroponic method using a porous foam plate. More particularly, it relates to a hydroponic method which involves cultivating plants on a porous foam plate disposed on a water surface, the porous foam plate consisting of an aggregate of foamed resin beads, such as polyethylene or polystyrene, bonded to one another with continuous open spaces among adjacent beads, and to a container used therewith.
2. Description of the Prior Art
Hydroponics, sometimes called "aquiculture", is a process whereby plants are cultivated in water containing dissolved inorganic nutrients necessary for the growth of vegetables and other plants.
When it is desired to stabilize or support the stalk of a plant grown by such a hydroponic method, the conventional practice relies on the use of pebbles or an open celled polyurethane foam. According to the hydroponic method using pebbles which is illustrated in FIG. 1, a pot 2' is so supported by a plate 2 so that its lower part is located underwater 1, as shown in FIG. 1, pebbles 3 are placed therein, and the seeds of a plant 4 are sown in the pebbles. This method, however, suffers from the following defects.
1. Direct seeding causes the individual seeds to be situated at different depths, so that non-uniform budding or plant growth occurs.
2. Thinning of seedlings may result in moving the pebbles, and consequently may exert a harmful influence upon neighboring seedlings.
3. During thinning, the roots of the seedlings tend to be cut off. The roots remaining among the pebbles as a result of cutting rot and adversely affect the other seedlings.
4. In the case of radishes, the root portions grow very deep among the pebbles, and cannot be seen from the outside, which can lead to a selection of an inappropriate harvesting time.
5. In re-use, the pebbles need to be disinfected. Furthermore, since they are heavy, their handling requires a large amount of labor.
On the other hand, according to the hydroponic method using a polyurethane foam which is illustrated in FIGS. 2a and 2b, the seeds of a plant 4 are sown and grown on an open celled polyurethane foam sheet 5 disposed on the water surface, as shown in FIG. 2a. Root hairs 4b of the plant 4 growing from the joint of a stalk 4a (the area where roots grow from the stalk, which corresponds to the boundary between the soil and the open atmosphere in soil culture) extend into the polyurethane foam, and absorb water and nutrients. This method, however, has the following defects.
1. Since water is impregnated in large quntities into the entire area of the polyurethane foam sheet 5, the joint of a stalk 4a tends to become excessively laden with moisture, and, consequently, the root is liable to rot.
2. In view of disadvantage (1), the joint 4a must be placed apart from the polyurethane foam sheet 5 as the plant grows, which requires extra labor.
3. As in the case of using pebbles, the roots of the plant are susceptible to breakage at the time of thinning. As a result, the roots remaining in the polyurethane foam sheet 5 rot, and adversely affect other seedlings.
4. In the cultivation of radishes on the polyurethane foam sheet 5, lateral roots 4d occur as is shown in FIG. 2(b).